1. Field of the Invention
This invention relates generally to the field of computer graphics and, more particularly, to a graphics system configured to compute blending functions for overlapped video projectors.
2. Description of the Related Art
For large format visualization applications, especially for group presentation, or for immersive virtual reality display, it is often desirable to use several video projectors whose projected images tile a display surface. The surface may be curved or otherwise non-flat.
A major requirement for many of these visualization applications is that there be no seam or visual discontinuity between the regions displayed by the respective projectors. This is quite difficult to achieve, because of unavoidable differences in the brightness, color temperature, and other characteristics of the projectors, and because of the human visual system's sensitivity to visual artifacts having high spatial frequency, such as abrupt boundaries.
To overcome these problems, the projected areas are often overlapped to some extent (e.g., 10 to 25% per linear dimension) and a gradual transition is accomplished between the content displayed by one projector and its neighboring projector(s). Overlapping the projected areas requires further processing of the video content displayed by each projector, so that the overlap areas are not brighter than the non-overlapped areas. (The brightness perceived in an overlap area is an optical sum of the brightness profile of each projector hitting the overlap area.)
Typically, within an overlap area, the video intensity of each projector will be gradually diminished as it approaches the boundary of its region. The contribution of one projector will ramp down as the contribution from its neighboring projector ramps up. Since tiling can be done both horizontally and vertically, overlap areas may occur on the sides, top and bottom of an image projected by a single projector. The processing of video to accomplish this ramping is commonly known as “edge blending.”
An installation with three projectors arranged to project onto a flat surface is shown in FIG. 1. An installation with three projectors arranged to project onto a curved display surface is shown in FIG. 2.
Edge blending overlaps usually consume a significant percentage of the screen area so that the transitions occur with a low spatial frequency. Human vision is comparatively insensitive to low spatial-frequency artifacts.
Edge blending may be accomplished by weighting digital video RGB values provided to each of the projectors. The weights may be chosen to achieve (or approximate) the condition of uniform brightness over the whole visual field (i.e., the union of all regions) as suggested in FIGS. 3 and 4.
Nonuniformities in perceived intensity may be induced by means other than region overlap. For example, consider the installation shown in FIG. 5. Across the field of projector C, the screen distance varies considerably. Intensity varies as the inverse-square of distance. Thus, there will be a significant change in the intensity due to projector C across region C.
Therefore, there exists a need for systems and methods capable of compensating for the nonuniformity of perceived brightness in display systems composed of multiple overlapping projector images.